This application relates generally to communication systems and, more particularly, to a method and apparatus for load balancing in communication networks.
Referring to FIGS. 1, 2a, 2b, and 3, an illustrative embodiment of a conventional code division multiple access/high data rate (CDMA/HDR) communication network 10 may include a packet data service node (PDSN) 12 that is operably coupled to the Internet 14 and a base station controller (BSC) 16 that is operably coupled to access points (APs)18a, 18b, and 18c. Access terminals (ATs) 20a, 20b, and 20c in turn may be operably coupled to one or more of the APs 18a, 18b, and 18c. 
As will be recognized by persons having ordinary skill in the art, a CDMA/HDR communication network typically utilizes a combination of time division multiple access (TDMA) and CDMA. In an illustrative embodiment, each communication channel is shared among several users, but on an as-needed basis rather than a fixed time slot as in TDMA. An example of a CDMA/HDR communications network is the wireless communication network available from Qualcomm, Inc. that, in an illustrative embodiment, provides a 2.4 Mbps data rate in a standard 1.25 MHZ CDMA bandwidth.
During operation of the network 10, in an illustrative embodiment, an active set 22 of APs may communicate with the AT 20a utilizing a wireless forward communication link 24 and a wireless reverse communication link 26. In an illustrative embodiment, at any given time period, only one of the APs in the active set 22 may communicate with the AT 20a in the forward communication link 24. By contrast, in the reverse communication link 26, the AT 20a may communicate with one or more of the APs in the active set 22. As will be recognized by persons having ordinary skill in the art, the active set 22 of APs may include one or more APs 18.
Furthermore, during operation of the network 10, in an illustrative embodiment, in the forward communication link 24, the APs 18 may transmit a power control signal, a pilot signal, and/or a data payload to the ATs 20 using a power control channel 24a, a pilot channel 24b, and/or a data payload channel 24c, respectively. As will be recognized by persons having ordinary skill in the art, the forward communication link 24 may include a plurality of power control signals, pilot signals, as well as other conventional signals. In an illustrative embodiment, the power control signal controls the power of the signals transmitted by the corresponding AT 20. Thus, in this manner, the power level of signals transmitted by a particular AT 20 is controlled by one or more of the APs 18. In an illustrative embodiment, in the reverse communication link 26, the ATs 20 may transmit data rate control signals to the APs 18 using a data rate control channel 26a. In an illustrative embodiment, the data rate control signal controls the rate of data transmitted by the corresponding AP 18 to a particular AT 20 as a function of the carrier to interference ratio (C/I) for the pilot signal transmitted by the corresponding AP to the particular AT. Thus, in this manner, the rate of data transmission from a particular AP 18 to a particular AT 20 is controlled as a function of the calculated C/I for the pilot signal that was transmitted from the particular AP 18 to the particular AT 20.
In a typical CDMA/HDR network, as illustrated in FIG. 3, an AT 20a may communicate with a plurality of APs, 18a and 18b, and each AP, 18a and 18b, in turn may service one or more additional ATs 20 within corresponding wireless cells, 22a and 22b. One of the shortcomings of such conventional CDMA/HDR networks is that the APs, 18a and 18b, may be unevenly loaded. Thus, the available capacity for data transmission from the APs, 18a and 18b, to the ATs 20 serviced by the APs may be uneven. As a result, the level of data throughput from the APs, 18a and 18b, to the AT 20a may be less than desirable.
The present invention is directed to improving the load balancing of CDMA/HDR communication networks.
According to one aspect of the present invention, a method of load balancing in a CDMA/HDR communications network including one or more access points capable of servicing an access terminal is provided that includes the access terminal monitoring the quality of the forward communication links between the access points and the access terminal, the access terminal monitoring the capacity utilization of the access points, and the access terminal requesting data transmission from a selected one of the access points as a function of the monitored quality of the forward communication links and the monitored capacity utilizations of the access points.
According to another aspect of the present invention, a method of determining a forward loading factor for an access point in a CDMA/HDR communications network including an access terminal and an access point is provided that includes monitoring forward activity bits for the access point for a predetermined number of time slots within a time window, counting the number of active slots for the access point, and calculating the forward loading factor for the access point by dividing the number of active slots by the total number of time slots.
According to another aspect of the present invention, a communications network is provided that includes one or more access points, and an access terminal operably coupled to the access points. The access terminal is adapted to: (1) monitor the quality of the forward communication links between the access points and the access terminal, (2) monitor the capacity utilization of the access points, and (3) request data transmission from a selected one of the access points as a function of the monitored quality of the forward communication links and the monitored capacity utilizations of the access points.
According to another aspect of the present invention, a communication network is provided that includes an access terminal, and an access point operably coupled to the access terminal. The access terminal is adapted to: (1) monitor forward activity bits for the access point for a predetermined number of time slots within a time window, (2) count the number of active slots for the access point, and (3) calculate the forward loading factor for the access point by dividing the number of active slots by the total number of time slots.
The present embodiments of the invention provide a number of advantages. For example, the present illustrative embodiments permit load balancing in CDMA/HDR communication networks. In this manner, CMDA/HDR communication networks may be more efficiently utilized. In addition, permitting the access terminal to select the access point to transmit data to the access terminal as a function of the quality of the forward communication link and the available capacity of the access points provides an efficient and reliable method of selection. Furthermore, the use of specific parameters such as the carrier to interference ratio and the forward loading factor permit the ATs 20 to efficiently and reliably calculate the selection parameter P.